1. Field of the Invention
The present invention relates to a battery pack consisting of at least two cells connected in parallel and/or in series together, and more particularly, to a battery pack adapted such that if any one of a plurality of cells incorporated therein becomes faulty, it is electrically disconnected from the normal other cells.
2. Description of Related Art
A small portable electronic apparatus such as a portable personal computer (will be referred to as xe2x80x9cportable PCxe2x80x9d hereinunder), personal telephone or the like uses a battery pack as a power source. Such a battery pack ordinarily consists of one or more up to 9 cells electrically connected in parallel and/or in series. For example, a battery pack destined for use as a drive power source for a portable PC has been proposed which incorporates therein three series-connected cell units each consisting of two cells electrically connected in parallel to each other (a battery pack of this type will be referred to as xe2x80x9c2-parallel/3-series battery packxe2x80x9d hereinunder). Assume that in such a 2-parallel/3-series battery pack, each of the cells has a capacity of 4 V, for example. A total voltage the battery pack as a whole can provide is 12 V (=4Vxc3x973) since the cells are connected in parallel together in each cell unit while three such cell units are connected in series together in this battery pack. Also, for example, a battery pack destined for use to drive a portable telephone has been proposed which consists of two cells electrically connected in parallel to each other (a battery pack of this type will be referred to as xe2x80x9c2-parallel battery packxe2x80x9d hereinunder).
In addition to the above types of battery packs, the conventional battery packs having heretofore been proposed include a one having to be able to supply a large current, for example, a battery pack destined for use as an electromobile drive battery and consisting, for such a purpose, of 10 or more up to 100 cells connected in series together. As such an electromobile drive battery, there has been proposed a one consisting of 48 cells, for example, electrically connected in series together (will be referred to as xe2x80x9c48-series battery packxe2x80x9d hereinunder). If each of the 48 cells has a capacity of 4 V, for example, the 48-series battery pack can totally provide a voltage of 192 V (=4 Vxc3x9748) since the 48 cells are connected in series together in the battery pack.
In addition to the above-mentioned 2-parallel/3-series battery pack for the portable PC, a battery pack in which three cells are electrically connected in series together (will be referred to as xe2x80x9c3-series battery packxe2x80x9d hereinunder) has also been proposed for use with portable PCs. It is assumed that in such a 3-series battery pack, each of the cells has a capacity of 4 V, for example. The battery pack as a whole can provide a total voltage of 12 V (=4Vxc3x973) as in the above-mentioned 2-parallel/3-series battery pack since the cells are connected in series together in this battery pack.
In the conventional battery pack in which at least two cells are connected in parallel together (which will be referred to simply as xe2x80x9cparallel-type battery packxe2x80x9d hereinunder), such as the above-mentioned 2-parallel/3-series battery pack, 2-parallel battery pack and the like, however, if any one of the cells becomes faulty, the whole battery pack cannot be used.
The above will be described more particularly below. If any one of the cells connected in parallel together in the above-mentioned parallel-type battery pack is internally short-circuited or otherwise fails, the discharge current from the normal other cells will continuously flow to the faulty cell. Thus, if the faulty cell is left as it is in the parallel-type battery pack, the voltages in the normal other cells connected in parallel to the faulty one will become 0 V in a certain time. That is to say, the failure of one of the cells in a battery pack will cause the battery pack to wholly be unusable.
Also in a battery pack in which at least two cells are connected in series together (will be referred to simply as xe2x80x9cseries-type battery packxe2x80x9d hereinunder) such as the aforementioned 48-series battery pack, 3-series battery pack or the like, if any one of the cells is internally short-circuit or otherwise fails, the battery pack cannot wholly be used.
More specifically, if any one of the cells connected in series together in the above-mentioned series-type battery pack is internally short-circuited or otherwise fails, it will generate abnormally much heat and thus become hot. Thus, in the series-type battery pack, if the faulty cell is left as it is, its temperature will continuously be elevated to a point at which the safety device for that cell is activated to electrically shut off a current to the faulty cell. Namely, if any one of the cells used in a battery pack becomes faulty due to such an internal shortage or the like, it will cause the battery pack to wholly become unusable.
Further, the series-type battery packs include a one having a function to monitor the temperature of each of the cells used therein. In the battery pack with the temperature monitoring function, however, when a temperature elevation of one of the cells incorporated in the battery pack due to its abnormal heat generation, the battery pack itself is judged to be abnormal and thus the charging and discharging are stopped, so that the whole battery pack becomes unusable.
Furthermore, as one of the series-type battery packs, there has been proposed a battery pack adapted to electrically disconnect any one of the cells used therein, which is found faulty, from the normal other cells. Assume for example that such a battery pack is applied to a 48-series battery pack destined to drive an electromobile. In this case, if one of the cells in the 48-series battery pack becomes faulty and the failure is detected, the current through the whole battery pack is interrupted and thus the battery pack is wholly unusable.
As will be understood from the foregoing, the larger the number of cells used in a battery pack, the higher the failure rate of the battery pack itself becomes. The battery pack has a correspondingly lower reliability. More particularly, the total failure rate of a conventional battery pack is a product of a failure rate of one of cells used in the battery pack and a number of the cells. For example, a battery pack using 48 cells of 0.1% in failure rate will have a total failure rate of 4.8%.
Accordingly, the present invention has an object to overcome the above-mentioned drawbacks by providing a highly reliable battery pack consisting of at least two cells and which can totally be used even if any one of the cells becomes faulty.
The above object can be attained by providing a battery pack comprising at least two cells connected in parallel together, having according to the present invention:
means for judging individually the cells to detect whether they are normal or faulty;
a cell or cells, if any thus found faulty, being electrically disconnected from the normal other cells.
In the above battery pack, the individual cells are judged to detect whether they are normal or faulty and a cell or cells thus found faulty is electrically disconnected from the normal other cells. The battery pack as a whole is allowed by the normal other cells to continuously work normally. Therefore, the battery pack has an improved reliability.
Also the above object can be attained by providing a battery pack comprising at least two series-connected cell units each consisting of at least two cells connected in parallel together, the battery pack having according to the present invention:
means for judging individually the cells to detect whether they are normal or faulty;
in the cell unit including a faulty cell or cells, the faulty cell being electrically disconnected from the normal other cells; and
in the cell unit including no faulty cell or cells, the normal cells as many as the faulty cells electrically disconnected from the normal other cells in the cell unit including the faulty cells, being electrically disconnected from the other cells.
In the above battery pack, it is possible to prevent a voltage imbalance between the two or more cell units, thereby permitting a safety use of a battery pack comprising many cells.
Further the above object can be attained by providing a battery pack comprising at least two cells connected in series together, having according to the present invention:
means for judging individually the cells to detect whether they are normal or faulty; and
a cell short-circuiting means consisting of a first switching element connected in series to each of the cells, and a second switching element connected in parallel to each of the cells via a current interrupting element. This battery pack is adapted such that, when the cell failure detecting means judges any one of the cells to be faulty, the first switching element in the cell short-circuiting means is shifted from a connected position to a disconnected position from each cell to interrupt a current line to each cell while the second switching element is shifted from a disconnected position to a connected position to short a circuit portion corresponding to a current line connected to the faulty cell.
In the above battery pack, only a faulty cell is electrically disconnected from the normal other cells in such a manner that the latter will be charged and discharged. Thus the battery pack is allowed to continuously work normally with an improved safety.
These objects and other objects, features and advantages of the present intention will become more apparent from the following detailed description of the preferred embodiments of the present invention when taken in conjunction with the accompanying drawings.